Getting an organ transplant could add four or more years to your life, according to an analysis of the United Network for Organ Sharing (UNOS) records published in JAMA Surgery. Data on 1 million possible transplant patients over the past 25 years showed that 533,329 people got transplants, and more than 2 million years of life were saved overall.

More than 123,000 people are on waiting lists for organ transplants in the United States, 100,000 of whom are waiting for new kidneys. Yet the need for healthy organs far outpaces donations. Only 28,000 transplants were completed in the last year, according to the 2014 national data from the U.S. Organ Procurement and Transplantation Network. Only half of these were kidney transplants. Each day, 18 Americans die waiting for an organ transplant.

When you or a loved one faces organ failure, you’ll want to know all you can about the complexities of donation and transplantation — whether it’s a new kidney or, more rarely, a liver, heart, pancreas, lung, or intestine transplant. Your new organ could come from a living donor. Alternatively, it may come from a person who had arranged to donate their organs after death. Today, as many as 100 million in the United States are signed up as organ donors in the event of their death, notes the Department of Health and Human Services.

Here are 10 facts your doctor might not tell you about organ transplants and donations:

1. Transplanted organs don't last forever.

While transplanting a healthy organ to replace a diseased or failed organ can prolong life, transplants have limits. A transplanted pancreas keeps working for five years in only 57 percent of patients, meaning nearly half of patients will need a second transplant. A transplanted liver will function for five years or more in 70 percent of recipients, and even longer if the organ came from a living donor. After a heart transplant, the five-year survival rate for the organ is about 76 percent. However, a transplanted lung continues to work for five years or more in only about 52 percent of patients, according to the Scientific Registry of Transplant Recipients.

2. A transplanted organ can carry a hidden disease along with it.

Before transplant, organs are screened for common infections and diseases. This is to exclude any potentially dangerous contamination. Still, one or two people out of every 100 who receive an organ transplant — up to 560 people in the United States each year — contract a hidden infection or disease along with it, data from the U.S. Centers for Disease Control and Prevention shows. Infectious diseases linked to transplants include viral, bacterial, fungal, and even parasitic illnesses. A few examples are West Nile virus and rabies virus, as well as undetected hepatitis B and hepatitis C viruses missed during screening. Rare cases of cancer from transplants have also been reported.

3. The cost of donating an organ as a living donor may be too high for you.

Offering to donate a kidney or part of your liver as a living donor can be life-saving, but the process may come with surprisingly high costs. Donating an organ could mean lost pay from time away from work, travel costs for surgery, medical care after the procedure, and time off to recover. Current estimates are that living kidney donors in the United States bear out-of-pocket, transplant-related costs of $5,000 to $20,000. The number of people willing to be living kidney donors has been going down, and this may be in part because of the high financial burden. Lower-income people are much less likely to donate a kidney, according to a 2013 analysis of more than 50,000 donors.

An unexpected consequence of donating an organ as a living donor is a change in your eligibility for insurance coverage. The Affordable Care Act ensures that you can't be denied health insurance. But a 2014 survey of people who were living kidney donors found that, in many cases, they were turned down for life insurance coverage. Other donors were surprised to find they were charged higher health and life insurance premiums after donating.

5. Transplant tourism may be risky for your health and unfair for organ donors.

U.S. law prohibits paying people to donate organs, but the practice is not banned globally. People who travel to other countries to have organ transplants may not realize that their donor could be an unwilling participant — a prisoner, refugee, or illiterate person — notes an international declaration on organ trafficking. A study of transplant patients in California found that those who went to China, Iran, and the Philippines for the surgery usually received organs from living but unrelated people in those countries. They also took a risk with their health by having a transplant in another country. Thirty percent of transplant tourists lost the organ due to rejection versus 12 percent in the United States. In addition, 52 percent of transplant tourists in the study returned home with severe infections.

6. A liver transplant won’t cure an infection like hepatitis C.

Each year, 6,000 Americans out of the 17,000 who need one have liver transplants, according to the American Liver Foundation. The leading cause of liver failure in the United States is hepatitis C viral infection. But if you get a liver transplant, the new, healthy liver can become infected with hepatitis C once inside your body. This is because the hep C virus can continue to circulate in your blood throughout your body, including your liver.

7. A kidney transplant may be a real option for you if you have kidney failure.

If your kidneys are failing, your doctor should discuss the option of kidney transplant with you before you start on dialysis, as part of informed consent. This discussion is even required on provider claims for Medicare and Medicaid reimbursement. But one-third of dialysis patients surveyed said they didn’t know about the transplant option, found a Johns Hopkins University study published in August 2014. As far as the patients recalled, that mandated kidney transplant discussion never happened. Because the study showed that people informed about a transplant option are three times as likely to have one, be sure to ask about all your options, including transplant.

8. Women aren't as likely to be evaluated for kidney transplants, or get living-donor transplants.

Most women on dialysis who need a kidney transplant get offers from family and friends willing to donate a kidney. But fewer women than men go through with it, a 2014 survey of dialysis patients in Philadelphia showed. The reasons are unclear, but only about half as many women as men were ever evaluated by their healthcare providers to get the organ transplant process going. Researchers also found that women felt less willing to go through with a living-donor transplant, compared to a transplant from a deceased donor.

9. You could be too obese to have a transplant.

The American Society of Transplantation advises patients to get their weight down before a transplant, to a BMI of 30 or less. This corresponds to less than 203 pounds for a person who is 5-feet 9-inches tall. When you are obese, you may have more health problems after a transplant than someone who weighs less, a review of studies found. Obese people are more likely to have infections at the wound site of a transplanted kidney, and the new organ fails to function more often as well. People who are obese are also at greater risk of developing heart disease after a transplant compared to people who weigh less.

10. Where you live may determine how long you have to wait.

Your wait time for an organ may be from days to years, and doctors cannot predict the timing for any individual case. It depends on when an organ becomes available and whether it is the right fit for your blood type and body. Wait time can also be affected by where you live, data show. In the United States, people living in the Southeast have the highest rates of kidney failure and the longest waits for kidney transplants, found a 2014 national analysis by Emory University in Atlanta. The study reported that people living in New England have the shortest wait times.